1. Field of the Invention
The present invention relates generally to power management, power conversion and batteries and, more particularly, to power conversion for batteries.
2. Related Arts
Most of the electronic devices today are configured for specific battery types and chemistries. The selection of which chemistry to use is usually based upon an assessment of, among other considerations, the device's environmental conditions and expected lifetime, and the price of the battery at time of design.
Different batteries have different chemistries, each having their own properties, advantages and challenges. One conventional type of battery, that is used extensively especially in lower-end products, uses a Nickel-Cadmium (Ni—Cd) chemistry. A Ni—Cd battery has numerous drawbacks and limitations: it allows only moderate energy density (45-80 Wh/Kg); has a high rate of self-discharge of approximately 20% per month; and requires charging maintenance in the form of periodic charge/discharge cycles in order to prevent memory-effects which limit the usable capacity of the battery. Furthermore, the compounds used in its production are highly toxic and cause environmental problems. Cells of this chemistry have an output voltage of approximately 1.25 volts. The Nickel-Metal-Hydride (NiMH) chemistry is a variation of Ni-Cad and shares many of the Ni-Cad properties. It provides a slightly higher energy density 60-120 Wh/Kg.
In the recent years, Lithium-ion (Li-ion) batteries have become prevalent, especially in devices which require high energy densities such as laptops, medical devices and cell-phones. This chemistry provides high energy density (150-190 Wh/Kg) and is environmentally friendly. However, it also suffers from numerous drawbacks. It has a limited life and after 300-500 cycles the battery's capacity drops to 80% of the rated capacity. It has very low tolerance to overcharging, and if mistreated might become thermally unstable and hazardous. In order to maintain the battery's safety, it is essential to have charge/discharge monitoring and protection circuits that prevent over-discharge, monitor the charging process and stop the charging before over-charge. Cells of this chemistry have a maximum output voltage of approximately 4.1V but will provide efficient power at approximately 3.6V, and their voltage shouldn't drop under 2.5V-3V, depending on the kind of Li-ion used.
There is continuous progress in increasing the capacity of different types of the Li-ion chemistry and new battery technologies, such as spinnel and Li-Polymer, keep emerging. These technologies, while similar to the regular Li-ion technology, may require adaptation of the hosting devices due to slightly different voltages or charge procedures.
Finally, there are radically new battery technologies in the making, such as nano-tube based batteries, which hold the promise of much higher charge capacities. However, because these batteries will have electronic properties different from the currently common batteries, the current electronic products would need an adaptation circuit in order to benefit from such batteries.
As set forth above, most electronic devices are configured for a specific battery type. Locking the design of an electronic device into one specific battery type prevents the device owners from enjoying the benefits of new battery technologies, price reductions and other advances. In order to enjoy such benefits, the device must be re-designed in order to fit the new batteries. This is not desirable for the buyer.
Furthermore, if problems are found in the battery management circuits, a recall may have to be made in order to fix the problem. Recalls, that happen not infrequently, are costly to the device manufacturer.
Energy efficiency in analog conversion circuits is greatly dependant upon the current consumption. The conversion efficiency will usually be high for the designed load and current consumption, but as the load changes the efficiency drops. Thus, if good energy efficiency is desired, the conversion circuit must be specifically designed for the host device. Building a voltage-converting circuit to fit many different products and, thus, many different loads, is complicated and results in a large converter that is not suitable for a small battery.